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| FS Class 685 | |||||||||||||||||||||||||||||||||||||||||||||||
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 FS locomotive 685.089 in 2010 | |||||||||||||||||||||||||||||||||||||||||||||||
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The Ferrovie dello Stato (FS; Italian State Railways) Class 685 (Italian : Gruppo 685) is a class of 2-6-2 'Prairie' express train steam locomotives. These are colloquially known as Regine ('Queens' in Italian), mirroring their fame as one of the most successful and appreciated Italian steam locomotives. [1]
The Class 685 was the simple-expansion and superheated version of the pre-existing FS Class 680 locomotive, the premier express locomotive in Italy up to that date; while discarding the complicated compound feature, the 685 nonetheless kept the unusual feature of having the cylinders arranged in pairs, with each pair being served by a single piston valve with crossed ports (a feature typical of the Plancher engine of the Class 680 and other Italian locomotives). [2] [3]
The first 106 locomotives were built up to World War I, and had right-hand drive; construction resumed in 1920, and the remaining 165 were all built, up to 1928, with left-hand drive and a slightly longer boiler. Of the latter, 30 were built from the beginning with Caprotti valve gear, after it had been tested first on a FS Class 740 locomotive and then on other four 685 locomotives; all of these were initially reclassified as FS Class 686 locomotives, but were later placed again into the Class 685. [4] [2] [5]
The Class 685 was present on all the Italian mainlines before their electrification, thanks to its good performance related to its moderate axle load. It was renowned as a well-balanced design, especially for its very smooth riding qualities, and was almost universally appreciated. Despite being express locomotives, especially in the waning years of the Italian steam they proved to be apt for freight train pulling as well. [6] [7]
The maximum authorised speed for the Class 685 locomotives was originally 110 km/h (68 mph) and from 1932, it was raised to 120 km/h (75 mph). [8]
The first units to be withdrawn from service, in the mid-1960s, were the heavier S.685 locomotives, and the more maintenance-requiring Caprotti and Franco-Crosti locomotives; the last unit in active service, the 685.222, was withdrawn in early 1975. [9] [7]
The by then-obsolete FS Class 680 locomotives were first subjected to a first rebuild, in which 91 of them were superheated but kept the compound engine (with some of them receiving a larger high pressure (HP) cylinder); after it was determined that these locomotives were still inferior in terms of performance and water and coal consumption, it was decided to rebuild them into Class 685 locomotives, instead. [10] [11]
The first group of 31 locomotives, renumbered as 685.3XX, received the superheater and a simple-expansion engine, while keeping the original boiler pressure of 16 kg/cm2 (15.7 bar; 228 psi); they resulted in being even more powerful than the original Class 685s, thanks to their higher boiler pressure. A further group of 40 locomotives, with the new classification of 685.5XX, also received the Caprotti valve gear, and had a boiler that achieved even higher steam temperatures, to further improve their efficiency; some even received an exhaust injector.
| FS Class S.685 | |||||||||||||||||||||||||||||||||||||||||||
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 FS locomotive S.685.600 as preserved | |||||||||||||||||||||||||||||||||||||||||||
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The last batch of rebuilds, intended to serve on major lines on which the original axle load limits had been rescinded, were therefore subjected to an increase of their adhesive weight (by shifting the pivots of the Italian bogie and the trailing axle towards the driving axles) to improve performance, bringing their axle load up to 17 tons, and, taking advantage of the more relaxed weight limits, were fitted with a Knorr pre-heater; some of them also received a larger tender with a total water capacity of 29,000 L (7,700 US gal), used by the FS Class 691. In total, 49 were rebuilt until 1933, while in 1934 a 685.500, was further converted into a S.685. Based on their increased performance (comparable or, in some cases, even superior to the larger FS Class 690 Pacifics), they were classified as the separate Class S.685 ('S' standing for Speciale).
The Class S.685 locomotives mainly operated on the Milan-Venice, Milan-Turin and Rome-Naples (through Cassino) mainlines, especially on the former together with the FS Class 691. After these lines were electrified, respectively in 1958 and 1961, their increased axle load and maintenance needs led to their withdrawal by 1968. [12]
In total, 120 ex-Class 680 locomotives were eventually rebuilt, until 1933, bringing the total number of locomotives in the Class to 391. [13] [14] [15]
In 1939 five locomotives (amongst those fitted with Caprotti valve gear) were rebuilt with Franco-Crosti boilers; initially classified into the Class S.685, in 1951 they were reclassified as FS Class 683. [16] [17] [18]
In 1933 the locomotive 685.410 had her cylinders replaced by a large forward motion steam turbine and a smaller reverse turbine; this experiment, under the guidance of renowned engineer Giuseppe Belluzzo, was completely unsuccessful, and the locomotive was restored to its previous condition in 1934. [19] [20] [21]
Five Class 685 locomotives survive into preservation:
The Franco–Crosti boiler is a type of boiler used for steam locomotives. It was designed in the 1930s by Attilio Franco and Dr Piero Crosti. The main difference between it and conventional feedwater heaters widely used on the continent is that the Franco-Crosti boiler uses both exhaust steam and exhaust gases from the firebox. Conventional feedwater heaters only use exhaust steam.
The Ferrovie dello Stato Class 625 is a class of 2-6-0 'mogul' steam locomotives in Italy. The class is commonly known by the nickname Signorine, or Signorina in the singular, because of their perceived grace and beauty compared to other locomotives.
The Ferrovie dello Stato Class 740 is a class of 2-8-0 'Consolidation' steam locomotives.
The Ferrovie dello Stato Italiane Class 691 is a class of 4-6-2 'Pacific' locomotives; they were the fastest and most powerful steam locomotives ever built for the Italian railways.
The Ferrovie dello Stato Class 640 is a class of 2-6-0 'Mogul' steam locomotives in Italy. Commonly nicknamed "Signorine", a nickname shared with the similar Class 625, these locomotives were the first superheated steam locomotives in Italy.
The Rete Adriatica Class 500, classified after 1905 in the Ferrovie dello Stato Italiane as Class 670 was an unorthodox and iconic cab forward 4-6-0 (2'C) steam locomotive.
The Ferrovie dello Stato Italiane Class 690 was a 4-6-2 'Pacific' steam locomotive for express trains.
The Ferrovie dello Stato Italiane Class 746 is a class of 2-8-2 'Mikado' steam locomotive. These were the biggest steam locomotives ever built by the Ferrovie dello Stato, even though not the fastest, which were the Class 691s.
The Ferrovie dello Stato Italiane Class 470 is a 0-10-0 steam locomotive.
The Ferrovie dello Stato Class 480 is a 2-10-0 steam locomotive.
The Ferrovie dello Stato Italiane Class 650, formerly SFAI1181-1200 and Rete Mediterranea 300 Class, also known as "Vittorio Emanuele II", was the first steam locomotive in continental Europe to have the 4-6-0 'Ten-Wheeler' arrangement.
The Ferrovie dello Stato Italiane Class 680 is a 2-6-2 express steam locomotive; it was the direct ancestor of the very successful and appreciated Class 685.
The Ferrovie dello Stato Italiane Class 600, formerly Rete Adriatica Class 380 and Società per le Strade Ferrate Meridionali Class 380, is a 2-6-0 'Mogul' steam locomotive; it is considered by some as the first Italian modern steam locomotive.
The Ferrovie dello Stato Italiane Class 835 is a 0-6-0T steam locomotive; it was the standard steam shunter of the FS.
The Ferrovie dello Stato Italiane Class 290, formerly the Rete Adriatica Class 350 bis, is a 0-6-0 steam locomotive.
The Ferrovie dello Stato Italiane Class 310, formerly Rete Mediterranea Class 380, was a 0-6-0 steam locomotive; they were the first Italian as-built compound locomotives.
The Ferrovie dello Stato Class 741 is a class of 2-8-0 'Consolidation' steam locomotives, rebuilds from the FS Class 740 with a Franco-Crosti boiler; it was the last class of steam locomotives introduced in Italy.
FS Class 400 were steam locomotives of French construction, built for service in Italy. They were 0-8-0 tender locomotives with two outside cylinders.
The Ferrovie dello Stato Class 745 was a class of 2-8-0 'Consolidation' steam locomotives.
The Ferrovie dello Stato Class 744 is a class of 2-8-0 steam locomotives; they were the last orthodox steam locomotives built for the FS.
